This invention relates generally to roadway barriers, and more specifically to an improved method and apparatus for interconnecting roadway barrier segments to minimize lateral displacement upon impact.
One type of moveable roadway barrier system is adapted to be lifted by a mobile transfer vehicle and moved to a selected position on a roadway. Moveable barrier systems of this type find particular application at roadway construction sites and on roadways and bridges where the groupings of incoming and outgoing lanes of traffic must be varied, such as is common during commute hours.
The barrier system itself comprises a series of interconnected concrete and steel modules hinged together to form a continuous chain. The cross-section of each module is similar to that of other types of roadway barriers, and may have a T-shaped top section. A standard module has a height of approximately thirty-two inches, a length of approximately thirty-nine inches and a weight of approximately 1400 pounds. The modules are pivotally connected together by inserting a steel pin through hinge components attached to the ends of each adjacent pair of modules.
The self-propelled transfer vehicle includes a conveyor system for shifting the barrier system laterally across the roadway from a first side to a second side of the vehicle. The shift or lateral displacement of the barrier system can be normally varied from four to over twenty-six feet. The conveyor system includes a plurality of guide and support wheels or rollers that function to engage beneath the T-shaped top section of the modules for lifting and transfer purposes.
The modules move through a serpentine-like transfer path (i.e., an elongated xe2x80x9cSxe2x80x9d curve) for accurate positioning thereof to define a repositioned lane line. The modules are moved at a speed approximating five miles per hour through the conveyor system. Oftentimes, the transfer vehicle must negotiate curved sections of roadways whereby the barrier system is likewise curved.
U.S. Pat. Nos. 4,806,044 and 4,828,425, both assigned to the assignee of this application, each address the long-standing problem of providing a barrier system that will elongate or contract to accommodate positioning of the system at varied radii on a curved roadway. The original barrier system, disclosed in U.S. Pat. No. 4,500,225, is particularly useful for straight-line roadway applications and utilizes a hinge connection between each adjacent pair of modules. The hinge connection includes aligned circular holes, formed in overlying hinge plates, adapted to receive a hinge pin therethrough. However, even when the holes are lined with a thin (e.g., xe2x85x9xe2x80x3 wall thickness) elastomeric bushing, the modules may not elongate as a unit when the system is moved radially on a curved roadway.
For example, it has been determined that when the barrier system is moved from a 2,000 foot radius to a 2,012 foot radius, the composite length of the barrier system must increase by approximately 0.214 inches for each barrier segment (of 3.28 feet, pin to pin) of the barrier system to effectively accommodate this new position on the same, curved roadway. Conversely, repositioning of the barrier system radially inwardly to a new position on the curved roadway, having a radius of curvature of 1,988 feet, will require a corresponding contraction of the composite length of the lane barrier system. In the above example, it should be understood that the ends of the barrier system are preferably located at the same relative radial position on the curved roadway thus require the aforementioned composite elongation or retraction of the system.
One solution to the latter problem of compensating for curvatures of varied radii on a curved roadway has been to substitute elongated slots for the pin-receiving circular holes, formed in the hinge plates. The slots allow the lane barrier system to assume various radii, as described in the above example. However, it has proven further desirable to return the spacing between each adjacent pair of modules to a nominal one when the barrier system is loaded onto a transfer vehicle and thereafter returned to its normal position on a roadway, e.g., the above-mentioned radius of 2000 ft.
Repeated transfer of the modules, having slotted hinge plates, will tend to xe2x80x9cstack-upxe2x80x9d the modules towards one of the ends of the lane barrier system which may interfere with effective transfer and placement of the modules in their correct positions. In particular, it is desirable to maintain the pivot pin between each adjacent pair of modules at a centered position therebetween (and reestablish the nominal spacing) when the barrier system is returned to its nominal position on a roadway. This feature, when achieved, facilitates the efficient transfer of the system by the type of transfer and transport vehicle described in the above-referenced patents.
The invention described by above-referenced U.S. Pat. No. 4,806,044 addresses this problem by providing elastomeric pads in the hinge connections, between each pair of adjacent modules of the barrier system, whereby the modules will: (1) elongate or contract to assume a composite varied length different from their nominal composite length in response to the imposition of a load on the system, and (2) return the modules to their nominal composite length when the load is removed (i.e., self-centering hinges). The invention described by U.S. Pat. No. 4,828,425 addresses the problem by preloading the hinges, connecting adjacent pairs of modules together, to facilitate a high degree of uniform spacing between the modules when they are moved through the conveyor of a self-propelled transfer vehicle for subsequent replacement on a roadway.
Duckett U.S. Pat. No. 4,815,889 teaches a lane barrier system with a pivot control connected to at least one of the hinge connections between barrier modules, and permitting the pivot axis to move between the modules whereby the overall length of the connected modules, is capable of elongating or contracting. Thus, the elongation and contraction is accomplished by the hinge connections, and not the barrier itself.
When impacted by a vehicle, the lateral displacement of a chain of barrier modules immediately starts to occur which induces tension into the entire chain as the hinges become xe2x80x9ctwo-blockedxe2x80x9d (i.e., solidly locked together). As the lateral movement increases, the tension in the chain increases and a force resisting the lateral movement is developed. However, and as described supra, a chain of barriers must have the ability to increase or decrease the circumferential length to allow the chain to be moved outwardly or inwardly from a given radius of curvature on a roadway. Because of this requirement, each barrier hinge should have the ability to expand or contract a nominal distance (e.g., one-half inch). Therefore, upon impact, the barrier will move laterally until each hinge is xe2x80x9ctwo-blockedxe2x80x9d and the tension in the barrier chain is adequate to overcome the lateral force.
The above-referenced methods of hinge connection result in a barrier chain that is subject to greater lateral displacement upon impact by a vehicle than the current invention. Such lateral displacement can be problematic, especially in situations of high impact severity.
The purpose of this invention is to eliminate the allowance of additional space in each hinge between each barrier while at the same incorporating some other mechanism which will allow the chain of barriers to become longer or shorter when it is necessary for the radius of the chain to be increased or decreased. This invention utilizes individual hinge mechanisms between each barrier module such that when the barrier chain is deployed on a roadway, the barrier modules will be maintained at all times in a metal to metal contact (two-blocked), that is, in a condition which will cause the barrier chain to go immediately into tension upon any lateral movement (such as by a vehicle impact).
The preferred system utilizes two principal elements:
1. A capstan drive system on the transfer machine which will maintain a slight degree of tension as the barrier chain is deployed; and
2. At least one variable length barrier module in the barrier chain which includes a hydraulic or mechanical mechanism which allows it to expand or contract in length (and which may be spring biased to a preferred position) to allow for the required geometric changes during the transfer process, but which will be locked into position in the deployed position so that it cannot expand when the chain of barrier is put into tension from a vehicle impact. It is this second element which is the subject of this application.
The inventive method and apparatus minimizes the lateral displacement of a series of interconnected barriers (e.g., concrete with steel reinforcement, or steel with concrete filling) when impacted by a vehicle with an extremely high impact severity, such as is required by the NCHRP testing procedures to assure that the vehicle will not penetrate the barrier. Although this invention relates primarily to a xe2x80x9cpermanentxe2x80x9d moveable barrier system, the principle is also applicable to a xe2x80x9ctemporaryxe2x80x9d type of moveable barrier system.